This invention relates to method and apparatus for determining the existence of certain operating conditions in excavating machinery or the like on the basis of data related to the position of the machine's operated implement. More particularly, the invention relates to means and method for determining the onset of and preventing a tightline condition in a dragline excavating machine or the like.
A principal tool in surface mining operations is the large walking dragline which removes vast amounts of overburden material in order to expose valuable minerals to be mined. In order to enhance the efficiency of such machines, they have been made larger and larger in size and in their load-carrying capabilities or bucket capacities. Consequently, the control systems used on the machines have become increasingly sophisticated in order to improve dynamic response time and decrease digging cycle time. This has increased the workload on the operator and has probably made the operator more susceptible to error.
Due to their particular geometry, all draglines are inherently susceptible to a condition termed "tightlining". Such a condition is defined as being that condition where the amount of hoist and drag rope paid out creates a condition where the ropes become tight and the bucket is drawn toward the boom structure at an undesirable velocity. The latter condition is termed dynamic tightlining. A condition termed static tightlining can occur when the bucket is carried too close to the boom. A dragline becomes particularly vulnerable to static tightlining in mining operations where deep digging, selective overburden removal or unique mining plans or terrain require the operator to carry the bucket close to the boom to provide adequate working clearances.
In the case of dynamic tightlining, the bucket actually approaches the boom at a velocity such that collision with the boom will result if proper action to stop the bucket is not initiated within a minimum time dictated by the velocity and position of the bucket. A dragline bucket is controlled by two independent motions termed hoist and drag. The hoist and drag ropes, for whatever reason, may be commanded to travel in essentially opposite directions, which will produce a resultant bucket velocity directed toward the boom structure. If this situation were not controlled, the bucket and/or ropes would ultimately contact the boom structure and, remembering that the bucket is a sizable item, it can be expected that extensive damage will occur.
In the case of static tightlining, the operator, for any of the reasons discussed above, is generally caused to carry the bucket close to the boom making it very difficult for the operator to view the operation of the bucket and its proximity to the boom structure. When the bucket is being carried so close to the boom, any side-by-side movement can lead to contact with and subsequent damage to the boom structure. The lateral movement of the bucket does occur during acceleration and deceleration of the machine while swinging to dump due to the large inertia of the suspended bucket.
In either case, the damage is usually substantial and can only be repaired after taking a dragline out of service. The costs of repair and lost use of the dragline are monumental.
Electromechanical systems are presently available for sensing the onset of a tightline condition. Of necessity, such systems utilize wireropes, springs, turnbuckles, etc. and such mechanical components are highly subject to vibration and fatique. In the operating environment of a dragline, they will receive much of the latter. Under operating conditions, such electromechanical systems have been found to be self-destructive. They are subject to deterioration caused by vibration, shock and the elements. Moreover, no known electromechanical system is capable of sensing the onset of a dynamic tightline condition as described above. The known electromechanical systems require the use of wireropes attached to the boom structure in as close proximity as possible thereto without interfering with the digging operation. The position of this wirerope continually requires adjustment and is in danger of destruction. The electromechanical systems have relatively slow response times due to the fact that they must operate using spring constants and inertias and experience wirerope stretch.
It is, therefore, an object of this invention to provide method and apparatus for sensing the existence of certain operating conditions based on data related to the position of the machine's operating implement. More particularly, for sensing the onset of both static and dynamic tightline conditions and for providing protection against the consequences of such condition.
Another object of this invention is to provide method and apparatus for static and dynamic tightline protection which will not affect the performance capabilities and efficiency of the protected dragline.
A further object of this invention is to provide a method and apparatus for sensing and protecting from a tightline condition which provides a control response in the shortest possible time with the greatest possible degree of accuracy.
Still another object of this invention is to provide a method and apparatus for tightline sensing and protection which is capable of operating in any machine environment and is capable of operating with any size or type of such machine.
A further object of the invention is to provide a method and apparatus for tightline condition sensing and protection which is capable of operating in the harsh environment customarily experienced by excavating or mining machinery or the like in a reliable fashion and which is easily maintainable.
The foregoing and other objects are obtained in accordance with the invention in a method and apparatus for sensing and preventing a condition related to the position of the operated implement, such as a tightline condition in a dragline or the like. In order to derive the necessary data with which to compute the operating condition in question, the amounts of hoist and drag rope paid out are sensed. The sensed values of hoist and drag ropes paid out are added to produce a sum signal having a value proportional to the sum of the amount of the hoist and drag ropes paid out. In order to determine the existence of a static tightline condition, this sum is compared with a predetermined constant which is determined in accordance with machine geometry. If the result of that comparison is that the sum signal is less than the predetermined constant, machine operation is halted due to the existence of a static tightline condition.
In a second comparison, the aforementioned sum signal will produce an indication only if a velocity limit has been exceeded and the sum of the feet of rope off the drums is less than or equal to a predetermined constant. The constant being based on machine geometry and machinery time constants.
In addition, in an alternate form, the sum signal can be compared with predetermined constants to provide limit indications. A first comparison is made to provide the operator with an indication that the bucket is close to the boom point. Another limit indication occurs when the bucket has been lowered a predetermined distance. Both of the above comparisons are based on information with respect to hoist motion. The data regarding drag rope paid out is used for providing analogous limit indications.